6.0l - Lost #3 Cyl. While Hauling

[middle_road]

2000 Silverado 2500 6.0l 4WD 123k

 

I've lost the left bank I fear. Need assistance determining cause, if possible.

I'm trying to figure out what the devill happened to #3 cylinder.

Getting ready to tear it down tomorrow and was looking for

insight/suggestions/guidance at to what to watch/look out for.

 

I was hauling our 8000# camper down I75 this past weekend when things went bad.

It started with a bit of surging going uphill @ 4200rpm, then a couple of hills

later hesitation, with a nasty vibration started and the SES light started flashing.

Limped home the last 60 miles.

Very poor acceleration but up past 2000rpm she would go.

Tore into it yesterday and found #3 spark plug gone.

It's an Autolite AP5245. (Picts at bottom of post)

 

Replaced all with AC/Delco Rapidfire #12's.

Nothing improved. Very rough and she's tossing p0300 errors.

(and there was a p0303 before I changed the plugs.)

Cleared them out and they don't come back for 10-20 minutes of runtime.

And there is now a 'knock'. *SIGH*

 

Tests/diagnostics performed:

 

Compression test:

No.1 - 100#

No.3 - 35# <--- This can ruin your day

No.5 - 125#

No.7 - 105#

 

No.2 - 150#

No.4 - 135#

No.6 - 145#

No.8 - 145#

 

Coil packs tested statically - all good

Fuel Pressure tested - met spec.

Nothing out of the ordinary from the exhaust.

 

TIA

[8.1HD/ALLISON]

doesn't sound good.... I can tell you from experience, never run different brand plugs than what it came with.... have seen many misfires caused by that. Good luck with your repairs

[desrtrat]

looks like your piston may have a hole in it. if lucky maybe just a valve(s) need replacing. ether way just guessing...

 

good luck

[wierdo124]

regardless, in order to find the problem it's obvious it'll need a teardown if your compression is that low. Just get her done.

[middle_road]

Update:

Removed the heads and found a 'Stretched' intake valve on #3.

The face of the head of the valve is concave by about .10".

I have never seen a valve do this.

 

Cylinder wall is in great shape, and can't find any other obvious signs

for the low compression on the drivers side.

 

Heads are now in the shop. I'm going to replace all the valves, not trusting

GM stock parts right now. Magna Flux should show any cracks.

 

Does anyone have any insight as to a cause for this?

 

Thanks,

_mr

[kdixer]

A while back I rebuilt an atv that dropped a valve due to running too lean and overheating the valve. You could possibly have a lean condition on that cylinder which is causing it to burn too hot and heating the valve to the point of distortion. Just a thought...

[desrtrat]